In a layer two (L2) network, the spanning tree protocol (STP) is applied to avoid the loops that result in broadcast storm and break down the entire layer two network. The STP prevents the loops by detecting the redundant links that could form loops and blocking these links in the layer two network. The STP is an IEEE standard, 802.1D, and has been implemented in all the layer two switches.
The waste of the bandwidth of the blocked links is a drawback of the STP. In the highly mesh or fabric network topology, which is more and more popular in the data center network, there exist a lot of redundant links and therefore STP causes a huge amount of waste of the bandwidth. The Multiple Spanning Tree Protocol (MSTP) allows a separate spanning tree for each VLAN group. The MSTP could improve the bandwidth utilization rate if there are a lot of VLAN groups and each of them selects different alternative path. However, the MSTP requires more complex configuration than the STP and the bandwidth utilization could still be poor if there is only a few number of VLAN groups or the STP instances of these VLAN groups select common paths among all the possible alternatives.